A muffler arrangement having a flow duct is intended to eliminate or at least mitigate the disturbing generation of noise and stimulation of vibrations which are caused by a flow, for example an air and/or gas flow, in a flow duct.
Disturbing vibrations, for example of the intake housing and of the muffler arrangement, are to be largely avoided.
Disturbing vibrations are generated particularly when an undesirable swirling of the flow medium occurs in the flow. Particularly when the flow duct is operated with different operating pressures and/or operating velocities of the flow medium, for example the intake housing of a gas turbine, where the pressure and/or the velocity of the intake air fluctuates sharply, depending on the required power output, measures for the avoidance of, in particular, self-excited vibrations are difficult, since these should take into account every operating situation.
Known muffling measures include, for example, the arrangement of a number of muffler elements in the flow duct, for example plates, as a result of which essentially the flow is to be led along a desired path through the flow duct, in order to alleviate undesirable swirlings and the vibration problems associated with these.
However, when the operating conditions, such as, for example, the pressure and/or the flow velocity of the flow medium, vary while the flow duct is in operation, it often happens that the flow which is established deviates seriously from the desired path, for example as a result of a minor disturbance. Due to the undesirable and usually asymmetric pressure conditions which are then established, even the muffler elements themselves are often excited to vibrate.
Examples of known arrangements of this type, which present problems in terms of an undesirable excitation to vibration of the muffler elements, are arrangements of a plurality of rows of muffler elements, arranged one behind the other in the direction of flow, transversely to the direction of flow, the muffler elements themselves being arranged longitudinally in relation to the direction of flow.
The next row following a preceding row can then be arranged so as to be offset transversely (“staggered”) or not offset transversely (“in line”) with respect to the preceding row.
In the first case, the flow, for example an airflow which is led between two muffler elements of the preceding row, is apportioned, in particular symmetrically, to the two flow corridors formed by the adjacent three muffler elements of the next row, in the case of low flow velocities.
Beyond a specific flow velocity, beyond a specific power stage with regard to a gas turbine, the disturbances in the flow are such that the airflow is apportioned randomly and unevenly, so that, in an extreme situation, only one of the abovementioned two flow corridors of the next row leads the airstream further on, and the airstream may oscillate between the two flow corridors.
The asymmetric pressure conditions which are then established may then bend one or more muffler elements to one side, until, when a specific bending angle is exceeded, the muffler element abruptly swings back and the flow conditions are thereby violently changed (“flip flop effect”).
Such excitations of the muffler elements themselves are undesirable, since they may be transmitted to the surrounding flow duct and to further components in the surroundings and, for example, may lead to damage.
With regard to the muffler rows arranged “in line”, the same effects may occur, but usually beyond higher flow velocities, as compared with the first instance. Although “in line” arrangements have a higher lower limit for the flow velocity beyond which the abovementioned undesirable effects occur, they are nevertheless inferior, in terms of their muffling properties, to the muffler rows arranged so as to be offset transversely, since, in an “in line” arrangement, a direct rectilinear sound path through the muffler rows is possible.